Maki,
I have just come upon your site for the first time today, when I was googling 'nagaimo.' I quickly read a number of your informative pieces and recipes, and I am soooo impressed by your articulate well infomed writing style and your very helpful user-friendly attitude. I have a few questions and so appreciate your help.

When i purchased nagaimo today at my local asian market , there were long tubers for $4 lb. and flatttened blob shaped nagaimo for $17 lb. Plse help me understand what might be the flavor difference between those 2 nagaimo(that would explain their price difference?) I bought the nagaimo for yama kake. Are nagaimo and taro really the same thing or is it simply that 'yam' gets used to name scores of different tasting tubers? It doesn't resemble taro I have worked with!

Also, one of the nagaimo recipes i googled mentoned treating nagaimo to a short vinegar water bath to counter a chemical. Is that chemical the same that can cause itchiness and if so, is it countered just as well by wrapping the tuber around the outside when grating it- to avert skin contact with the tuber skin?

When I make dashi and follow the traditional instructions which call for "bring to boil and turn off and.".........., the result is too weak for my taste. I end up doing the unthinkable and simmering the katsuobushi for 15 or 20 minutes, until the dashi has more flavor. I do not detect any bitterness from this. Am I crazy?
Thanks much for your help.

The long straight kind of root is nagaimo, and probably (though I can't be sure since I haven't actually seen it - photographs would help in this case) the flat roundish one is another kind of a similar root called yamatoimo. Yamato imo would be more expensive because it's rarer, and more dense/less watery.

Yamaimo and taro are NOT the same thing, to me. The root that is called taro most of the time is satoimo - look up satoimo - see my how to. But, people use the terms 'yam' and 'taro' so casually to refer to any old unidentfied root, it's hard to tell.

You could post the URL of that page you found about the vinegar so I could read it to see where and how they are recommending its use...vinegar is used often in its preparation, but again, I DON'T KNOW WHAT THEY WERE SAYING so how can I tell? :)

For dashi, you can boil it a bit or add mroe katsuobushi if it's too weak for your taste. There are no hard and fast rules in cooking, only what works for you! I remember on the old Japanese Iron Chef program, that Chef Rokusaburo Michiba (imo the best Iron Chef ever) used to make the commenters/audience gasp by putting HUGE amounts of katsuobushi in his dashi pans, instead of a delicate handful. It worked for him, certainly!

As to the dashi question, I am not Japanese, but I also either add more bonito flakes to my dashing or I leave it to steep a little longer, usually, adding more vs longer. I also notice that the longer I steep the kombu the richer the flavor of the overall dashi turns out, so I usually let that steep at least 30 mins in almost boiling water.